Avalanche Studios' exploration-and-combat adventure was launched as a single-player title in 2010. A multiplayer mod has been available from the JC2-MP mod team website since last year.
"Installing the mod is very easy now that we're on Steam," offered a note from the JC2-MP team. "You will be able to download and install it from the Steam store page. Everyone will be able to host a server and configure it exactly how they want."